Telegraph system.



0. D. VI. GUTHE.

TELEGRAPH SYSTEM,

APPLICATION FILED IAN.2, I9Is.

25.4.6.5. 9.Io.II

UNITED sTATEs PATENT oFEIoE,

OLOF D. M'. GUTHE, OF NEW YORK, N. Y., ASSIGNOR T0 `WESTERN,:ELECTRIC COMPANY, INCORPORATED, OF NEW YORK, N. Y., A CORPORATION OF NEW YORK.

TELEGRAPH SYSTEM.

Specification of Letters Patent.

Patented Nov. 18, 1919.

Application filed January 2, 1918. Serial No. 209,968.

To all whom t may concern.'

Be it known that I, OLoF D. M. GUTHE, a citizen of `the United States, residing at New York, in the county of New York, State of New York, have invented certain new and useful Improvements in Telegraph Systems, of which the following is a full, clear, concise, and exact description.

This invention relates to telegraphic systems, and more particularly to systems for rendering secret telegraphic service.

The principal object of this.- invention is to provide an improved organization of apparatus for applying cryptography to the transmission of telegraphic messages.

In order that telegraphic -messages ofza confidential nature .may be intelligible only to an addressee or to the immediate attendants at the telegraphic st-ations, various systems of fixed codes have been developed, but in case the key for decipher-ing such a code should fall into the hands of unauthorized parties the cryptic value of the code would thereby be annulled. As a precautionary measure in safe-guarding secret communications, it is the usual practice to vary or entirely change the code at frequent intervals, to insure that message impulses while under transmission, may be unintelligible to persons who may unauthoritatively cut-in on or tap the telegraphic circuits. of cryptographic telegraphy may therefore be said to depend on the frequency andthe facility with which a secret code may be changed or varied.

This invention has for its object an arrangement applicable to systems o f printing telegraphy in which each character transmitted is represented by a definite combination of current impulses, as in the Baudot code, and provides for changing the code at the transmitting and receiving 'station simultaneously by means of a sequence switch or similar device operated automatically whenever a given circuit combination occurs. Such a circuit combination may for example occur whenever a particular letter (or letters) of the alphabet is transmitted and by its occurrence complete a circuit to move the sequence switch to a new position. In each new position of the sequence switch a change is made in the circuits con- The effectiveness and the utilitynecting the transmitting apparatus, whichA determines the combination of impulses to be transmit-ted, to the distributer which sends the impulses of the combination to the line sequentially. For each new position of the sequence switch, therefore, the impulses of a given combination are sent to the line in a different order from that provided by the previous quence switch.

The receiving station is similarly equipped with a sequence switch which moves in step with the sequence switch at the transmitting station and rearranges the impulses of the character combination so that they will act upon the receiving selective apparatus in the vproper order to bring about the printing of the desired character. y

This 'invention is illustrated diagrammatically `in the accompanying drawing, and for the sake of clearness only so much of a telegraphic equipment has been shown as will be necessary to a ready understanding of the system.

oIn describing this invention, a transmitting equipment located at a 'first station indicated by the reference character A is connected by means of a line conductor L with a receiving equipment located at a second station B. At the first station, a group of five transmitter contacts' C control the operation of a group of five transmitting and switching relays D which serve to establish different current polarities with five segments of a distributor E, and also to prepare circuits for the control of a sequenceswitch equipment comprising the various arts indicated by the reference numerals 0 to 95, inclusive. From the distributer E the line conductor L extends to the distant station, and terminates through a polarized relay 37 of a polar duplex equipment which includes an artificial line AL. The line relay 37 controls the electrical energization of the switching circuits of a. receiving distributer F, tive segments-of which are connected to control live receiving and switching relays of a group G'. In addition to establishing operations whereby impulses received from the transmitting station ma be recomposed into a` message record, pre erably in the form of a type printed sheet,

the relays G also prepare circuits corresponding with circuits already mentioned as effective through the relays D for the control of a sequence-switch equipment identical with and having its parts indicated by reference numerals similar to those employed with the sequence switch at the first station. of the respective sequence switches are connected intermediate the segments of the distributers and the associated relays D and G.

Before entering upon a more detailed description of this system, it Will be mentloned that the special features of the invention provide that in transmitting messages from the station A tothe station B, the first three transmitter contacts 20, 30 and i0 may, through control of the sequence switch at the first station, become effective in vari-- ous combinations to`cont-rol, respectively, the current condition of the first three segments 28, 38 and 48 of the distributer E. In a similar manner the sequence switch may transpose the control relation 'of the last two transmitter contacts 50 and 60 with Irespect to the last two segments 58 and 68 of this distributer. Coincident with changes in control relation between the transmitting contacts C and the segments of the distributer EI at the first station, the sequence switch at the second station also establishes corresponding control relation between the five segments of the distributer F and the live printed control relays G. For operating the sequence switch, control circuits prepared by the relays D become e'ective at an instant a brush 39 in its regular travel from left to right, establishes connection between two segments 73 and 74 of the distributer E to initiate movement of the sequence switch, whereby changes in the control relation of thetransmitting'contacts C with respect to the segments of the distributer E will be effected. Therefore, as the,

brush 39 continues forward and returns (the distributer may be considered as of a rotary type) over the five segments 28, 38, 48, 58 and 68, the polarities selectedly present at these segments will be successively es tablished with the line conductor L.

rfhe brush 59 of the receiving distributer F will be understood to be operated, by means not shown, in synchronism with the brush 39 of the transmitting distributer.

Therefore, the brush 59 completes a circuit through the segments 73 and 74 of the distributer F to render the sequence switch at that point effective in establishing operations identical to those of the distant sequence switch, whereby the tive segments 28, 38, 48, 58 and 68 will be connected to the five relays G in the same order in which the contacts C, or more strictly speaking, the relays D, may be connected to the five segments of the distributer E. It will be obvious that although various changes may At each station Contact membersl be made in the polarity permutations of five successive impulses due to changes ofcircuit relations established by the sequence switch at the transmitting station, the s equence switch at the receiving station w1ll establish circuit changes to restore the permutations to their .original order and thereby permit them to be properly reproduced by the receiving n'inter.

In more speci cally describing this system, the sequence switches may be of the usual power-driven relay type as commonly employed in automatic telephone exchanges orV similar switching systems.V A motor- `driven member 71 of a magnetic clutch 7() is adapted to be engaged by and impart motion to a rotative member 72 which operates a cam-carrying spindle or other suitable means (not shown) for establishing various combinations of circuit connections through the several Contact members 75 to 95, inclusive. As commonly understood, a switch of this type is adapted to assume various positions in a regular sequential order, and in keeping with the established nomenclature for such devices numerals placed alongside each Contact member indicate that the corresponding member and an adjacent contact lever are engaged during the time the sequence switch may be in any one of the positions indicated by the numerals. For example, the numerals 1 3, 7 and 9 alongside a contact member 88 indicate that this member will be engaged by a movable contact lever 87 during the time the sequence switch may be in either of its positions l, 3, 7 or.9. In a similar manner the contact during the time the sequence switch is in either of its positions 2, 5, 8 or 11, and the lever 87 will also make Contact with a member 90 when the switch is in either of its positions 4. 6, l0 or 12. As indicated by the numerals alongside the contact members 78 and 79, an associated vcontact lever 77 may make contact with these members singly or with both members at the same time.

A single exception to the above described relation of the Contact members is necessary, however, in the case of the contact members 75 and 76 which are adapted to govern the rotation of the sequence switch. These contacts are shown separated, which is their normal position, and the numerals alongside the member 76 indicate the positions of the switch in which these contacts will separate to cause the sequence switch to stop. in the present embodiment of the invention the sequence switch is adapted to stop in each of its positions; therefore, when the switch leaves its position l, due to current through its clutch magnet as momentarily 'established by the brush 3S) while passing over the segments 73 and 74;, the governing contacts and 76 engage vsegment 48.

and maintain the clutch magnet energized until the switch arrives at its position 2, whereupon these contacts are separated automatically and the magnet 70 denergized to permit the clutch members 71 and 72 to disengage and thereby cause the switch to stop.

A Amore thorough understanding of the system may be had through considering various definite combinations or positions of the apparatus; therefore, dierent permutations of character selecting impulses will now be assumed and traced through the various steps by which they may be trans# mitted from the station A to the station B.

Let it first be assumed that it is desired to transmit a character which is distinguished from .all other characters or signs through a permutation of five impulses in the order of successive reversals of current polarity, beginning with a positive impulse. The transmitter contacts C may be considered as adapted to be controlled by a suitably notated means, as a punched or perforated telegraph message tape; therefore, for the present assumed combination of impulses, the contacts 20, 40 and 60 will be closed, while the contacts 30 and 50 will remain open. y Current from a grounded battery 13 by way of the closed transmitter contacts will respectively establish initial operation of the relays 21, 41 and 61,'after wlhicl, current from a similar battery 14 becomes effective through the normal contacts of a lock-release relay 15 to act through the contacts 22, 42 and 62 in respectively retaining these relaysl operated, independently of the transmitting contacts. Let it now be assumed that the sequence switch is in its position 1, thereby completing several `circuits which will now be traced. The conventional plus and minus signs adjacent certain contact stops of the relays D, will be understood to indicate that these stops connect to correspondingly poled Vand grounded batteries (not shown) for supplying line currents for signaling. For the combination of impulses under consideration, a circuit may be, traced from a positive source by way of the contacts 23 of the relay 21 and the members 80l and 17 9ct the sequence switch to the segment 28 of the distributer. In a similar manner negative current through the contacts 34 of the relay 31 traverses the contacts 84 and 83 of the sequence switch to the second segment 38. Positive current over the contacts 48 of the relay 41 may traverse the contacts 88 and 87 of the equence switch to the third egativev current through the contacts 54 of the relay 51 and the contacts 92 and 91 of the sequence switch may reach the fourth segment, while positive current by way of the contacts 63 of the relay 61 and the contacts 95 and'94 of the sequence Asecond station will be connected over the switch reaches the fifth segment 68. In addit1on to the various signaling .circuits just traced through the switching members of the sequence switch, a control circuit routed through the contacts 25, 35, 45, 55 and 65 70 of the relays 21, 31, 41, 51 and 61, respectively, continues through the master contacts 78 and 77 of the control switch to the local segment 7 4 of the distributer. The purpose of this circuit will presently be apparent. As already mentioned, the sequence switch at the station B will always bein a position to correspondwith the position of the sel quence switch at the station A, and as similar characters of reference have been employed in so far as they may be applied to the equipment at each station, it may be readily seen that vfor the prese-nt, posit-ion 1 of the receiving distributer is connected to the five receiving relays of the group G in. the same order in which the live relays of the group D are connected to the five segments of the sending dist-ributer E at the first station. The local segment 74 at the master cont-acts 77 and 78 and a lead routed through contacts of the relays G which correspond with and which are labeled the same as the contacts of the relays D at the first station through which the corresponding control circuit of the sequence switch at that point `is routed, as already described.

At the sending station, the distributer brush 39 is adapted to tra-vel in a certain timerelation to the movements ofthe trans- '100 f mitter control tape; .,therefore, `following the completion of the polarity potentials with the five segments of the distributer, as already described, this brush sweeps over these segments and successively completes circuit therefrom to a collector ring 29.

From the ring 29 these impulses continue over the line circuit L, and in passing through the polarized relay 37 at the dist-ant station, cause the armature' of this relay 110 to bias to one side or the other, depending on .the polarity direction of' the impulses received.

In printing telegraph work` impulses of line current which effect operation of devices at the reproducing or printing equipment are usually referred to as -ma1'king impulses, while impulses that do alot" so result are termed spacing impulses. As arranged in the present system, posi- 120 tive impulses effect marking, while negative impulses correspond with spacing `intervals. Therefore, each positive impulse received :from over the line L positions the armature of the line relay 37 to connect a 125 positive battery 47 with a collector ring 49 of the receiving distributer F. ln a con- .erse manner, each impulse of negative current from thelineL will bias the armature of the relay 37 against its non-connected ory 13( idle right-hand stop, thereby disconnecting the collector ring 49.

In phase with the arrival at the station B of each of the tive impulses now .under consideration, the following individual operations or spacings will take place: For the first, third and ifth impulses the armature of the relay 37 will be' biased to establish the battery 47 with the collector ring 49; therefore, as the brush 59 successively passes over the corresponding` se ents 28, 48 and 68, positive current respect1vely traverses the contacts 179 and 80, 87 and 88, and 94 and 95, thence through the relays 21, 41 and 61, respectively, of the group G to earth. Since the second and third impulses are of negative polarity the armature of the line relay 37 will thereunder discon-l nect the ring 49', and although connections are present from the segments 38 and 58 through contacts 83 and 84, 91 and 92, respectively, of the sequence switch to earth through the windings of the relays 31 and 51, respectively, the brush 59 in passlng over these se ments is ineffective and these relays there ore remain inert. It will be understood 'that devices (not shown) controlled by the relays Gi may now respond in recomposing vthe ive intelligible impulses into a printed character or other sign for which they may represent the transmission combination as present inv the notation on the distant tape. A locking circuit identical with the locking circuit of the relays D at the first station is provided for' retaining any one of the relays G operated after they have been initially energized through the distributer, as described.

After passin from the fifth segment 68, the distributer rush at each station arrives over its respective segments 73 and 74, but neither brush will be effective to complete a circuit throu h its associated clutch magnet 70 at this tlme, since the circuit of these magnets stands-open at the contacts 65 of their associated relays 61. During the present trip of the distributer brushes neither one of the sequence4 switches may respond,

and eachswitch will therefore remain 1n its position 1.

It will be understood that after leaving their segments 73 and 74 the distributer brushes or other suitably timed mechanism of the systems, will complete circuits to respectively operate the lock release relays 15, thereby restoring the relays 21, 41 and 61 at each station.

For a second example, a combination of impulses will be assumed, whereby, after they have been disposed of, the sequence -switches will be moved to change the relation of thetransmitting relays D with respect to the segments of the distributor E, while corresponding changes will take place relative to the relation of the segments of ing relays Gr.Y Accordingly, a combination' of impulses in the order of a positive, a negative, a positive and two negative impulses will now be chosen. The transmitter contacts 20 and 40 will therefore be closed to operate therelays 21 and 41, while the contacts 30, 50 and 60 remain separated and the corresponding relays 31, 51 and 61 will therefore continue in their normal positions. Since the resent impulses will be established .with t e five segments of the distributer E by way of circuits already traced through the contacts of the sequence switch, and in turn be disposed of through the receiving equipment at the station B in a manner similar to that already described in connection with the first combination ofk impulses considered, attention will be directed at once to the moment when the distributer brushes will have arrived over the segments 73 and 74 of the sequence switch controlling circuits. At each station, a circuit will thereby be completed from a grounded battery 16 by way of the winding of the clutch magnet 70, segment 73, the respective distributer brush, segment 74, sequence switch contacts 77 and 78, the contacts 65,55, 45, 35, and to earth through the contacts 25, respectively, of the relays 61, 51, 41, 31 and 21. In responding to current through this circuit, the clutch magnet brings the clutch members 71 and 72 into'engagement, whereupon the spindle operatlng member 72 is initially moved to establish the governing contacts 75 and 76, and thereby continue the energization of the clutch magnet until the sequence switch arrlves at its position 2. At this point, the` contacts 75 and 76 separate to denergize the clutch magnet 70 and permit the sequence switch to come to rest in its position 2. It will be obvious that the sequence switch at each station will now be in the corresponding position 2. 'After the distributer brush at leach station has passed from the sequence switch controlling segments, the lock release relays 15 will be tion of impulses prepared and transmitted will'be varied from the regular order in which they appear in the punched tape.v For example, let it now be assumed that perforations in the tape representing a,

character identified by five alternately poled continue inert.

impulses, beginning with a negative impulse, will now be transmitted. .The transmitting contacts 30 and 50 will, therefore, be closed to operate the relays 31 and 51, while the contacts 20, 40 and 60 will remain separated and the relays 21, 41 and 61 will accordingly For the first impulse, negative current through the contacts 24 of the relay 21 may traverse the members 80 and 179 of the sequence switch to the first segment 28 of the distributer E. For the second impulse positive current through the contacts 33 of the relay 31 and the sequence switch contacts 89 and 87 reaches the third segment 48. For the third impulse, negative current through the contacts 44 of the relay 41 and the members 86 and, 83 of the sequence switch reaches the second segment 38. For the fourth/l impulse positive current through the contacts 53 of the relay 51Y and the members 92 and 91 of the sequence switch energizes the fourth segment 58, while for the fifth impulse negative current through the contacts 64 ofthe relay 61 may complete circuit through the members 94 and 95 'of the sequence switch to the fifth segment 68. Therefore, when the brush 39 sweeps over the five segments there will be transmitted to the line L, tive successive impulses in the order of two negative impulses, two positive impulses and a negative impulse, instead of the alternate negative and positive impulses corresponding 'with the settings of the transmitter contacts C as effected-by the control tape. These impulses will be repeated by the line relay 37 to the distributer F at the receiving station, in phase lwith the travel of the brush 59 over the manner similar-to that already described. Since thel segments of the distributer kF are connected over circuits of the sequence .switch to the lrelays G in a manner identical tothe lconnections just traced between the 45"/relays`D and the segmentsof the transmitting distributer E, it will be obvious that, as transmitted,'the first negative lmpulse will correspond with the interval the brush v59 maybe over the segment 28 which' is connected Ato the relay 21. For the' secondv negative impulse, however, the brush 59 willat a corresponding instant be over the second segment 38 which by the transposition .already describedis now connected to the third relay 41. On the brush arriving over' the third segment 48, the third impulse -being of positive polarity, the battery 47 will be ei'lective tov operate the second relay 31 which is now connected to the third segment. The fourth impulse being of positive larity, the brush 59 arrives over the JIh. segment 58 in phase therewith and completes a connection to permit the battery 47 to operate the fourth relay 51, while the iifth impulse of negative current corresponds /e segments of that distributer in a4 with the instant the brush 59- will be over vthe segment 68 which isconnected to the httn relay 61. As described, negative vimpulses do not result in the operation of and 52 of the relays 31 and 51', respectively.`

Thus, it will be clear that although the order of the impulses in the combination just considered was disarranged between the time they were set up on the transmittin contacts C and the time they became e ective with the receiving distributer F at the distant station, the original or intelligible order was automatically restored at the time the impulses arrived at the receiving relays G. The latter relays, las positioned, are therefore effective to control the receiving devices (not shown) to reproduce the character or other operation corresponding with originating notation in the telegraph tape at the sendlng station.

fter the five message impulses have been disposed of as described, the distributer brush at each station passes over the segments 73 and 74, and although the three contact members 77, 78 and 79 of the sequence switch are now held together, the brushes are ineffective at'this time to establish current throuoh the respective clutch magnets 70. This 1s on account of the lead which extends from the member 78 being open at the contacts 25 of the relay 21, while the lead from theY member 79 stands open at the contacts 36 of the relay 31 as well as at the contacts 26 of .the,relay 21. Therefore, the sequence -switch at each station will remain in its osition 2 during the present trip of the distributer brushes. Immediately after the distributer brushes pass beyondl the segments 73 and 74, operations will take place to energize the lock release relays 15,and thereby denergize the relays 31 and 51 at leach station, as alreadyl de-v scribed.

i 4In addition to the control lead of the clutch magnet already described as routed 4from the sequence switch member 78 through certain normal and forward contacts of `the relays D or G, a second or branching lead already mentioned extending from the contact members 79 is routed through the contacts 6656, 46, 36 and 26 of the respective relays 61, 51, 41, 31 and 21 of these groups. In the present position 2 of the sequence switches, either one or the other of these circuits may become effect-ive to operate the associated clutch magnet, since the two leads are in Acontact with the lever 77. It may be pointed out that the sequence that for either of the last two impulse combinations, the relays 31 and 61 would remain unoperated. This will b e clear since two gap spaces as vthe normally separated contacts and 45 of the relays 21 and 41 are present in the first lead from the member V78, while the normally separated contacts 26, and 56 of the relays 21 and 51 are present in the second lead which extends from the member 7 9.

'In order that an actual'circuit may be traced through the second lead,.let it now be assumed that a character 'selecting com-V bination in the order of a positive impulse,

two negative impulses, a positive impulse anda negative impulse is prepared atfthe transmitting contacts C. The contacts 20 and 50 will vaccordingly be closed to operate the relays 21 andl 51, while thecontacts 30,

40 and 60 remain separated,A thereby continuing the inert condition .of the relays 31, 5l and 61. Following the -transmission and disposalof these impulses in a manner similar to the operations already described, the distributer brushes will arrive over their segments 73 and. 74. Atjeach station, a circuit will thereupon be completed to include the battery 16 in series with the clutch magnet. byway of the members 77 and 79 and the contacts 66, 56, 46, 36 and 26 of the respective relays 61, 51, 41, 31 and 21 to earth.. The sequence switch will be initially moved due to current through this circuit, to establish its governing contacts 75 and 76 until the switch arrives at its posit-ion 3,

when these contacts will separate to stopthe switch, all as previously described.

At each station, the position 3 of the sequence switches transposes the -connections between the first and second segments 28- and 38 and the irst and second relays 21 and 31, although'the third, fourth and fifth segments 48, 58 "and 68 are connected in regular order tothe third, fourth and fifth relays 41, 51 and 61. 1t will be mentioned that the five connections are respectively routed over the contacts 179 and 81, 83 and 85,87 and 8 8, 91 and 92, and 94 and 95 of the sequence switches. rlhe master contact 77 continues connected to the member79, but stands disconnect/ed from the member 78.

From the foregoing description it will be obvious that for certain positions of the se- Y may quence switch, either one of two characterselecting combinations of impulses may prepare circuits to permit a change of position by the sequence switch, as when the contact lever 77 is in connection with both of the members 78 and 79. For other certain posi tions of the sequence switch, as when the lever 77 may make contact only with either the member 78 or 79, it will also beI clear that"only.one or the other of the same two character selecting combinations of impulses be effective to prepare a circuit through which movement of the sequence switch may be ei'ected.

It will be understood that a transmitting equipment similar to the equipment A may be connected to a" lead 69 of the duplex equipment at the station B, and that by, providing a duplex equipment similar to.

that shown at B for terminating the line Lr at the station A, a receiving equipment at the latter station may be connected to respond to the transmitter mentioned for the station B. Two-way secret service would thereby be possible between the two stations.

Although the embodiment chosen for illustrating this invention has, for convenience, been based on a five-unit character-selecting code it will be obvious that the system may be employed with any code which may be based on a less or a greater number of im-V pulse units. Flexibility as to the frequency or percentage of changes in the transmission code as effected by the operation of the sequence switches will also be understood as depending upoh the particular letter or letters which may be chosen as represented by the impulse combinations whereby the initial preparation of circuit will be established through the contacts of the transmitting vrela' s or the receiving relays, to permit operation of the sequence switches. If letters which have a high percentage of use are taken as the units whereby the order of the sequence switch control contacts of the relays D or G are arranged, that is, such letters s e and s the transmission code Iwill be undergoing practically continuous ,and permutations of impulses for transmission, a distributer for transmitting the impulses of a combination to said line conductor sequentially, in combination with automatic means under the control of said transmitting apparatus for changing the sequential order of transmission of said impulses.

2. In a telegraph system in combination with a line conductor, means for preparing different combinations of impulses for transmission, means for sending said impulses to said line sequentially, and means operating automatically upon the transmission of a. particular combination of impulses to the line to change the order of transmission of the impulses of succeeding combinations.

3. In a telegraph system, a line conductor, a transniit-ting station comprising means for preparing different combinations of impulses for transmission, means for sending said impulses to the line sequentially, and means operating automatically when a particular combination of impulses is transmitted to change the 'order of transmission ot' the impulses of succeeding combinations, in combination with a receiving station comprising means, operated in step with said automatic means, to rearrange said impulses into the order in which they were originally prepared for transmission.

4. In a system of secret telegraphy wherein predetermined combinations of signaling impulses are prepared at transmitting contacts and impressed on a line by distribute'r means, means jointly controlled by said contacts and said distributer means for destroying the predetermined combinations of said impulses before they become effective with said line, l

5. In a s stem of secret telegraphy wherein unintelligi' le signals are received Ethrough distributer means and other electroresponsive means, means jointly controlled by said distributer means and said electroresponsive means for rendering said signals intelligible.

6. In a telegraph system, means for preparing signaling combinations comprising currents of different polarities, a line circuit, switching means for rendering said signaling combinations effective with said line, and other switching means controlled by said signal preparing means andthe first mentioned switching means to vary the order ot' the polarities forming said'signaling combinations before they are impressed on said line. y

7. In a telegraph system. means for transmitting unintelligible combinations of currents of different polarities, switching means, electrorcsponsive means conjointly responsive with said switching means in the reception of said combinations of currents, and other switching means under the control of the first mentioned switching means and said electroresponsive means for changing said combinations of currents into intelligi'ble signals.

8. In a telegraph system, means provided with teleg'aphic notation, first switching means controlled in accordance with said i notation, sources of dissimilar currents con- OLOF M. GUTHE. 

